(1) Field of the Invention
The invention relates to a pixel structure and a control system for controlling the pixel system, specifically to such a structure and such a control system which can improve chromaticity and brightness for the pixel.
(2) Description of the Prior Art
A liquid crystal panel primarily comprises a substrate, a color filter, and a liquid crystal layer between the substrate and the filter. On the substrate, there exist a plurality of thin film transistors arrayed and a control circuit in charge of displaying pictures or text. The color filter is used for mixing the three primary colors: red, green, and blue. As the liquid crystal panel cannot radiate by itself, an external light source is required to provide the display with effects on uniformity, high intensity, and broad viewing angle. According to the type of displays, plane light source can normally be divided into two categories, a back light module and a front light module, wherein the back light module, disposed at the back of a liquid crystal panel, is normally used for a transmissive display, while the front light module, disposed at the front of a liquid crystal panel, is primarily used for a reflective or a half-reflective display.
Regardless of either a reflective or a transmissive type for the liquid crystal display, if the absorption of a color filter or the density of pigments on the filter were too high, the transmissivity would decrease a lot. The brightness of the display is thus extremely limited, and therefore it needs to take the limit into account while designing a display of high brightness.
Please refer to FIG. 1A, showing explodedly a typical arrangement of pixels on a conventional liquid crystal panel. The conventional liquid crystal panel 10 has a bottom substrate 11, a top substrate 12, and a plurality of pixels 13. Each pixel 13 has a red sub-pixel 131, a green sub-pixel 132, and a blue sub-pixel 133. Each sub-pixel is a cubic structure. For example, the structure of red sub-pixel 131 has a photo-resistant layer 121 formed on the bottom surface of the top substrate 12, a thin film transistor 111, a pixel electrode 112 on the top surface of the bottom substrate 11, and a liquid crystal layer 14 in between the photo-resistant layer 121 and the pixel electrode 112.
Recently, to increase the brightness of liquid crystal 10, another sub-pixel of different color, such as a white one, is added to each pixel 13. As the backlight source (not shown in the figure) for liquid crystal panel 10 is normally white light, only a transparent area is added to the top substrate 12, thereby each pixel having four sub-pixels with colors: red, green, blue, and white. Existing arrangements for these four sub-pixels can be shown in FIG. 1B-1C, in both where a transparent photo-resistant layer together with three photo-resistant layers: red layer 121, green layer 122, and blue layer 123, is used for enhancing brightness of the pixel. FIG. 1B shows a stripe arrangement while FIG. 1C shows a mosaic arrangement.
Provided that the transmissivity of a material is 100%, because photo-resistant layers, 121, 122, or 123, have their own colors, only the light of the color can pass through. As to one of sub-pixels, 131, 132, 133, of three primary colors, only one of three color lights can pass through and therefore the amount of brightness is reserved by merely one third. As for pixel 13 consisting of sub-pixels, 131, 132, 133, of three primary colors, each transmissive area of sub-pixels, 131, 132, 133, occupies the transmissive area of pixel 13 by one third, and therefore the total amount of the transmissive light through pixel 13 is by one third (3×⅓×⅓=⅓). After transparent photo-resistant layer 124 is added to top substrate 12, pixel 13 now contains 4 sub-pixels where the transmissive area of each sub-pixel occupies the transmissive area of pixel 11 by one fourth. Provide that the transmissivity of transparent photo-resistant layer 124 is 100%, the total amount of transmissive light through such a pixel is by one half, which is great than one third (i.e, 3×⅓×¼+1×¼=½>⅓). This leads to changing the arrangement of pixels on top substrate 12 by substituting photo-resistant layers, 121, 122, 123, of three primary colors in addition to transparent photo-resistant layer 124 (RGB+W) for photo-resistant layers, 121, 122, and 123, of three primary colors (RGB). Transparent area 124 is used for increasing the amount of transmissive light such that all colors become brighter. However, the mixture of white light makes screen whiter and decreases the degree of color saturation.
As above mentioned, the brightness of liquid crystal display is limited by the transmissivity of photo-resistant layers. To increase the amount of transmissive light, it is required to add a white sub-pixel and then change the arrangement of pixels. However, because prior arts cannot effectively control the amount of transmissive light of white sub-pixel, after increasing the amount of tranmissive light through white sub-pixel, the saturation of sub-pixels of three primary colors is degraded. The present invention changes the pixel structure on a display and simultaneously applies circuit control to enhance the chromaticity and brightness for the display.